1. Field of the Invention
This invention generally relates to a database running on a computer network based on a client-server architecture. More particularly, this invention relates to a method and apparatus for managing a database through a remote data processing system including client nodes that access individual files managed by a server node.
2. Description of the Related Art
It can make more efficient use of a database to provide the same running on a computer network based on a client-server architecture controlled by, for example, a version of a UNIX (UNIX is a trademark of American Telephone and Telegraph, Incorporated) operating system and, to allow a plurality of client nodes to access a common or distributed database managed by a server node. For this purpose, the server node maintains database files. Likewise, the client node maintains application programs for requesting information or applications from the prospective server or servers. The client node executes these application programs to manipulate a database for changing information therein such as retrieving, appending and updating data. In this event, when the client node accesses a record file maintained by the server node for updating or appending data, control is passed to the server node and the client node is suspended until the former completes delivery of data. The client node can perform subsequent transactions only after it confirms that the server node can deliver the data without any trouble, i.e., data are properly updated or appended. Such confirmation-based operation is referred to as synchronous operation hereinbelow.
In the synchronous operation of the type described, the client node must wait for rendezvous with an output from the server node. In other words, the client node is hindered from performing any subsequent transactions until the server node completes its output operation. Accordingly, there is much overhead during communication processing which degrades the performance of the system.
It seems that so-called asynchronous operation may be a solution to this synchronization problem. When a client node sends a solicit message to the prospective server for updating or appending data, it can perform subsequent transactions without waiting for the server node to complete delivery of data. The performance of the system is improved because there is no necessity for rendezvous, hence the use of term asynchronous operation. However, the synchronization problem is not completely solved. Consider a database in which the data record contains data items prohibited from being defined over and again. It is impossible to notify the client node of the unexpected definition of the data item over and again. The data record may also contain a data item of a particular type (e.g., numerical values only). The client node will never be notified of data error caused by an attempt to obtain data of an inadequate type. The challenges include avoiding such inconvenience accompanying the asynchronous transaction. In this respect, an object of the present invention is to improve the above-described drawbacks and increase access speed to a database in a remote data processing system.